1. Field of the Invention
The present invention relates to an ink jet print head and more particularly to an ink jet print head suited for a suction-based recovery operation that involves drawing ink from ink ejection openings to keep an ink ejection performance in good condition or recover the original ink ejection performance.
2. Description of the Related Art
There are growing demands in recent years for higher print resolution and higher print speed in ink jet printing apparatuses.
Among the means to enhance the print resolution is a use of an ink jet print head (hereinafter referred to simply as a print head) which has nozzles arranged at high density. The nozzle generally includes an ink ejection opening for ejecting ink, an element to generate energy to cause the ink to be ejected, an energy application chamber accommodating this energy generation element to apply the generated energy to ink, and a flow path communicating with the energy application chamber to supply ink to the chamber.
One of the means to enhance the printing speed is to improve an ejection frequency of the ink jet print head. One factor that determines an upper limit of the ejection frequency of the print head is a time it takes for the nozzle to be refilled with a supplied ink after it has ejected ink (hereinafter referred to as a refill time). Thus, the shorter the refill time, the higher the ejection frequency at which the printing can be executed.
FIG. 1 is a schematic plan view showing a construction of a flow path used in a conventional ink jet print head. In this flow path construction, there is an energy application chamber (bubble forming chamber) 5 in which an electrothermal transducing element 1 is installed to cause film boiling in ink to generate energy for ink ejection. An ejection opening is provided to face the bubble forming chamber 5 in a direction perpendicular to the plane of the drawing (Z direction). Ink is supplied in a Y direction to the bubble forming chamber 5 through one ink path 7. Reference number 6 denotes a filter installed near an inlet of the ink path to filter out air bubbles and foreign substances to prevent them from entering into the nozzle. In a print head with this flow path construction, the refill time tends to be dependent on a pitch of the nozzles. That is, when the resolution is increased, the nozzles are arranged at high density, which in turn reduces the size of the liquid path, increasing the flow resistance of ink.
Another flow path construction, such as shown in FIG. 2, is known which is intended to reduce the refill time. In this flow path construction, two flow paths 7 are formed, one on each side of the bubble forming chamber 5, to allow the ink to be supplied from two directions, which reduces the refill time.
In the conventional ink jet print head of FIG. 1, since a flow path forming member 4 in the nozzle is arranged unsymmetrical with respect to an X direction center axis of the electrothermal transducing element 1, ink ejected in a Z direction may sometimes deviate in a direction not perpendicular to a plane of the electrothermal transducing element 1 but diagonally to it.
In the construction of FIG. 2 disclosed in Japanese Patent Laid-Open No. 58-8658, on the other hand, the flow path forming member 4 is symmetrical with respect to the X direction center axis of the electrothermal transducing element. So, the ink ejected in the Z direction can be made to deviate perpendicular to the plane of the electrothermal transducing element.
FIG. 3 is a conceptual diagram showing an example construction of a substrate of the ink jet print head with the flow path forming member 4 of FIG. 2. In this construction, nozzle arrays are arranged on both sides of one ink supply port 3 in the substrate. To the bubble forming chamber 5 of each nozzle, ink is supplied through an ink path 7 facing the ink supply port 3 and also through a common ink path 8 running parallel to, and at the far side or back side, of each nozzle array.
Generally, when mounted to a printer body, the ink jet print head performs a recovery operation to fill nozzles with ink and to remove air bubbles remaining in the nozzles. The recovery operation is executed by holding a cap member against an ejection opening-formed surface of the print head and depressurizing the inside of the cap member as by a pump to apply a suction force to the nozzles.
However, in the construction in which ink flows at the back of the nozzle arrays as shown in FIG. 3, air bubbles may get trapped in the common ink path 8. This is because ink is more easily supplied to the ejection opening directly through the ink supply port 3 than through the common ink path. Therefore, the ink flow is retarded, resulting in air bubbles remaining in the common ink path 8.
This phenomenon becomes more conspicuous as the number of nozzles allocated to one ink supply port 3 increases. For example, in a print head with 128 nozzles in one nozzle array, during the suction-based recovery operation, ink flows from both sides into the bubble forming chambers of a few nozzles situated at the end of the nozzle array. However, for the nozzles at the central part of the nozzle array, ink flows in mostly from the ink supply port 3 side, with only a small volume of ink flowing in from the common ink path 8. This is explained as follows. Since at the end of the nozzle array the distance from the ink supply port 3 to the common ink path 8 is short, the ink in the common ink path 8 flows easily. However, it becomes harder for the ink to flow as it moves toward the central part of the array. As to the ink flow into the bubble forming chamber when a suction force is applied, the flow from the ink path 7 facing the ink supply port 3 is dominant while the ink in the common ink path 8 is stagnant, sometimes almost not moving. As described above, in the common ink path 8, the ink flow is less active and bubbles may become difficult to remove.